/*
* AioContext wait support
*
* Copyright (C) 2018 Red Hat, Inc.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#ifndef QEMU_AIO_WAIT_H
#define QEMU_AIO_WAIT_H
#include "block/aio.h"
/**
* AioWait:
*
* An object that facilitates synchronous waiting on a condition. The main
* loop can wait on an operation running in an IOThread as follows:
*
* AioWait *wait = ...;
* AioContext *ctx = ...;
* MyWork work = { .done = false };
* schedule_my_work_in_iothread(ctx, &work);
* AIO_WAIT_WHILE(wait, ctx, !work.done);
*
* The IOThread must call aio_wait_kick() to notify the main loop when
* work.done changes:
*
* static void do_work(...)
* {
* ...
* work.done = true;
* aio_wait_kick(wait);
* }
*/
typedef struct {
/* Is the main loop waiting for a kick? Accessed with atomic ops. */
bool need_kick;
} AioWait;
/**
* AIO_WAIT_WHILE:
* @wait: the aio wait object
* @ctx: the aio context
* @cond: wait while this conditional expression is true
*
* Wait while a condition is true. Use this to implement synchronous
* operations that require event loop activity.
*
* The caller must be sure that something calls aio_wait_kick() when the value
* of @cond might have changed.
*
* The caller's thread must be the IOThread that owns @ctx or the main loop
* thread (with @ctx acquired exactly once). This function cannot be used to
* wait on conditions between two IOThreads since that could lead to deadlock,
* go via the main loop instead.
*/
#define AIO_WAIT_WHILE(wait, ctx, cond) ({ \
bool waited_ = false; \
bool busy_ = true; \
AioWait *wait_ = (wait); \
AioContext *ctx_ = (ctx); \
if (in_aio_context_home_thread(ctx_)) { \
while ((cond) || busy_) { \
busy_ = aio_poll(ctx_, (cond)); \
waited_ |= !!(cond) | busy_; \
} \
} else { \
assert(qemu_get_current_aio_context() == \
qemu_get_aio_context()); \
assert(!wait_->need_kick); \
/* Set wait_->need_kick before evaluating cond. */ \
atomic_mb_set(&wait_->need_kick, true); \
while (busy_) { \
if ((cond)) { \
waited_ = busy_ = true; \
aio_context_release(ctx_); \
aio_poll(qemu_get_aio_context(), true); \
aio_context_acquire(ctx_); \
} else { \
busy_ = aio_poll(ctx_, false); \
waited_ |= busy_; \
} \
} \
atomic_set(&wait_->need_kick, false); \
} \
waited_; })
/**
* aio_wait_kick:
* @wait: the aio wait object that should re-evaluate its condition
*
* Wake up the main thread if it is waiting on AIO_WAIT_WHILE(). During
* synchronous operations performed in an IOThread, the main thread lets the
* IOThread's event loop run, waiting for the operation to complete. A
* aio_wait_kick() call will wake up the main thread.
*/
void aio_wait_kick(AioWait *wait);
#endif /* QEMU_AIO_WAIT */
